A conventional valve opening/closing timing control device includes a lock mechanism and thus maintains the relative rotation phase at a locked phase even when a fluid pressure provided by a pump is low during start-up of the internal combustion engine. Moreover, after the start-up of the internal combustion engine, the valve opening/closing timing control device releases the locking by the lock mechanism and controls the relative rotation phase using the fluid that is supplied from the pump.
During start-up of the internal combustion engine, the lock mechanism is maintained in a locked state, but after the start-up of the internal combustion engine, it is necessary to quickly adjust the valve opening/closing timing by changing the relative rotation phase of the valve opening/closing timing control device.
To address this issue, Patent Document 1 discloses a mode of control in which during start-up of an internal combustion engine, one of an advancing chamber and a retarding chamber for displacing the relative rotation phase in an advance direction and a retard direction, respectively, of a valve opening/closing timing control device, is filled with a fluid, subsequently the other of the advancing chamber and the retarding chamber is filled with the fluid, and then a lock mechanism is unlocked.
Also, Patent Document 2 discloses a hydraulic control valve including an electromagnetic solenoid that controls the relative rotation phase of a driving rotating body and a driven rotating body of a valve opening/closing timing control device and that controls the lock status of a lock mechanism. This hydraulic control valve is configured so as to control the supply/discharge of a fluid to/from the advancing chamber and the retarding chamber as well as the supply/discharge of the fluid to/from the lock mechanism by operating a single spool using the solenoid.